JPS598799B2 - How to dispose of radioactive waste - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating medium and low level solid radioactive waste.

Solid radioactive wastes, such as reactor cooling aids of 1 uCi/ml or less, powders such as incineration ash of contaminated combustibles, and granules such as ion exchange resins, etc., are treated as concrete, One method of disposal was to mix it with asphalt, plastics, etc., solidify it, store it in containers such as drums, and then dispose of it in the ocean.

In general, standards for marine disposal of radioactive waste are determined by laws and regulations, such as the Act on Prevention of Radiation Hazards Caused by Radioisotopes, etc.
Article 9, Paragraph 2" and "Ordinance for Enforcement of the Act on Prevention of Radiation Hazards Due to Radioactive Isotopes, etc., Prime Minister's Office Ordinance No. 56 of September 30, 1960, Article 19, Paragraph 1, Item 8". For example, radioactive waste is sealed in a container, and the sealed container must be strong enough and corrosion-resistant to prevent damage during and after disposal, and the specific gravity when sealed in the container must be Items that do not meet standards such as being 12 or higher cannot be disposed of in the ocean.

On the other hand, among conventional solidification processing techniques, (1) When solidifying cement, aggregate and solid radioactive waste, for example, offshore super-aid for reactor cooling water, a large amount of reactor super-aid is mixed in. As the wiring becomes more difficult to cross, the amount of water required for the wiring increases, and as a result, breathing increases, making it impossible to expect the required mechanical strength.

In the case of furnace additive-cement assimilation, the mixing limit at which homogeneous mixing can be achieved and a certain degree of mechanical strength can be expected is 200.
1/rrl, the volume reduction property is very poor, and the mechanical strength (compressive strength) is about 100 kp/i, which is higher than the compressive strength required for marine disposal (15
okg/crit or higher).

Therefore, solidified cement such as Oki-Kousakusai is inappropriate as a method for solidifying solid radioactive waste.

(2) In addition, the conventional method of mixing and melting solid radioactive waste with asphalt or thermoplastic synthetic resin and cooling it to solidify it is based on asphalt or thermoplastic synthetic resin (e.g. polyethylene), filtering aid, and ions. Since the specific gravity of solid radioactive waste such as exchangeable resin is as low as approximately 1, if a container such as a drum containing solidified waste is damaged during ocean disposal, the solidified material may float and disperse, potentially spreading radioactive contamination. There are drawbacks such as.

In order to improve this drawback, when the solidified material containing radioactive waste and the container filled with it are separated, the solidified material itself has a specific gravity of 1.2 or more, which is higher than the specific gravity of seawater, and It is required to have physical or mechanical strength that can withstand impact upon landing on the bottom, water pressure after landing on the bottom, etc.

In terms of specific gravity, other than conventional solidified concrete, i.e.
Solid radioactive waste such as filtration additives and solidified materials such as asphalt and thermoplastic synthetic resins each have a molecular weight of approximately 1 to 1.1, and in this respect, unless the safety of containers such as drums is confirmed, they cannot be disposed of at sea. Disposal is not possible.

On the other hand, not only radioactive waste but also various industrial wastes are generated in large quantities in industry, and the safe treatment and disposal of these wastes has become a serious social issue.

Although these general industrial wastes are sometimes reused as industrial materials by taking advantage of their own characteristics, the majority of them are disposed of due to the huge amount of waste, the outflow of heavy metals, and pollution regulations such as dust. In many cases, it is difficult to decide on a method.

For example, in the nonferrous metal manufacturing and refining industry, the amount of waste from which valuable metals such as copper, lead, and zinc have been separated is enormous, and most of this waste is accumulated in places where it is deposited.

Of these slags, copper, lead,
Some separated materials such as zinc are used as construction materials, but most of them are stored in factories and then disposed of in landfills, etc., but today, with stricter pollution regulations,
The treatment and disposal of waste slag is also a serious problem, and a large amount of waste slag remains accumulated in factories, dumping grounds, etc.

The present inventors focused on the combination of radioactive waste and general industrial waste, and as a result of repeated studies on effective treatment and disposal methods,
By taking advantage of the properties of dry non-ferrous brick slag without impairing the excellent properties of asphalt or thermoplastic synthetic resins such as polyethylene, it has excellent physical properties required for solidified materials for marine waste disposal and is suitable for marine disposal. The present invention was achieved by discovering an economical method capable of industrial large-scale processing in which the solidified material itself has a specific gravity of 1.2 or more, which is a standard for the following.

Therefore, an object of the present invention is to provide a new method for treating and disposing of solid radioactive waste.

A further object of the present invention is to provide a new method for simultaneously ashing and disposing of solid radioactive waste and general industrial waste, particularly dry non-ferrous brick slag.

Furthermore, another object of the present invention is to combine reactor cooling water, reactor support agent for radioactive waste treatment, ion exchange resin and other solid radioactive waste flakes, asphalt or thermoplastic synthetic resin, and copper, lead, zinc. It is an object of the present invention to provide a method for treating and disposing radioactive waste that can be disposed of in the ocean by using slag and other tailings discharged from dry nonferrous metal manufacturing processes such as slag, etc.

That is, the present invention is characterized in that, in treating radioactive waste, the solid radioactive waste, asphalt or thermoplastic synthetic resin, and dry non-ferrous metal brick slag are melt-mixed and then cooled and solidified. do.

To further describe the present invention in detail, the method of the present invention involves the use of reactor cooling water, reactor aids for radioactive waste liquid treatment, powdered or granular ion exchange resin, flakes of other solid radioactive waste, or mixtures thereof and asphalt. Alternatively, it is characterized by melt-mixing a thermoplastic synthetic resin such as polyethylene and dry nonferrous metal brick slag, such as slag, adjusted to 5 mesh or less.

For this melt mixing, an extruder or the like may be used, or the three components may be mixed in a commercially available mixer, and then the mixture may be placed in a melting furnace and melted.

In any case, heat at a temperature of 150 to 200°C.

This temperature must be such that the radioactive waste and asphalt or thermoplastic synthetic resin do not carbonize and must be higher than the melting point of the asphalt or thermoplastic synthetic resin.For example, for polyethylene, it is preferably 160 to 190°C and 30 minutes after melting at this temperature. Mixing may be performed with stirring for ~2 hours.

The melted mixture is transferred from the melting furnace to an external container or a thermoplastic synthetic resin in a molten state.
Take out and cool to solidify.

The solidified material produced by the method of the present invention has radioactive waste, asphalt or thermoplastic synthetic resin, and dry non-ferrous metal brick slag uniformly dispersed, and the solidified material itself has a specific gravity of 1.2 or more. Compared to the specific gravity of the solidified material, which is a mixture of plastic synthetic resin and solid radioactive waste such as filtration aid, which is about 1 to 1.05, the specific gravity is higher than that of seawater, so it is unlikely that materials disposed of in the ocean will float to the surface. do not have.

Furthermore, the solidified material obtained by the method of the present invention is superior in physical and mechanical properties to conventional solidified material consisting only of asphalt or thermoplastic synthetic resin and solid radioactive waste.

Due to this specific gravity, physical and mechanical strength, the safety of the solidified material is maintained during marine disposal, and even if the container such as a drum is damaged, the solidified material can be safely disposed of.

Furthermore, the increase in specific gravity due to the mixing of dry nonferrous metal brick slag has the effect of shielding radiation emitted from radioactive waste, which is advantageous during handling, transportation, and storage.

In addition, the main components of dry non-ferrous metal brick slag, such as iron, silicon, and other metal elements, are in chemically stable forms such as silicic acid compounds or oxides, so there is no risk of marine pollution due to leaching of heavy metals. Although there is no danger, it is safer because the surface of the waste particles in the solidified body is covered with asphalt or thermoplastic synthetic resin.

The reason why the solidified material obtained by the method of the present invention exhibits such excellent performance is not clear, but the dry nonferrous metal brick slag particles used in the method of the present invention and asphalt or thermoplastic synthetic resin have a favorable interaction in the molten state. seems to be doing so.

That is, the slag discharged from, for example, a copper melt furnace, a zinc volatilization furnace, etc. used in the method of the present invention is heated to a temperature of several hundred degrees or more in the furnace and separated from valuable metals such as copper and zinc. Outside the furnace, the waste slag is rapidly cooled by water, etc., so the volume of the discharged slag rapidly shrinks, resulting in countless fine cracks not only on the surface but also inside the waste slag particles.

On the other hand, when asphalt or a thermoplastic synthetic resin, such as polyethylene, etc., is heated and melted, the viscosity decreases, and the molten asphalt or resin easily enters the voids of the waste particles, which have numerous fine cracks.

At this time, radioactive waste such as powder or granules also enters the voids together with asphalt or resin and is fixed in the voids of the tailings particles.

The main components of waste slag are silicic acid compounds and oxides such as iron, silicon, aluminum, calcium, and magnesium, which exist in a chemically stable form, so there is no risk of gas generation during melting, and the solidified material is extremely dense. state.

When the asphalt or resin in the molten state penetrates into the voids of the waste slag particles, it is adhered to the asphalt or resin and is homogeneously dispersed by the flow caused by stirring, and the dispersed waste slag particles become the central nucleus and cause some kind of dispersion. It is thought that this promotes the dispersion of radioactive waste, which has a small specific gravity, and makes it more homogeneous.

When the molten asphalt or resin hardens as it cools further, the waste particles act like aggregates in a state where they are completely bonded with the asphalt or resin, which prevents the physical and mechanical properties of the solidified material from deteriorating. It is thought that the

The present invention will be specifically explained below using examples.

Example 1 600 g of straight 6 0/8 0 asphalt was placed in an electrothermally heated mixed evaporator and stirred by a melting impeller at 170° C. 5.1 uCi/ru used for radioactive waste liquid treatment.
Ion exchange resin with a specific radioactivity of l (cation type: anion type - 1 = 2 weight ratio, water content 50 (wt%) soo
g and smelting slag discharged from a copper slag furnace (specific gravity 3.
3, Fe203 40%, 8102 39%, AI
2038%, Ca09%, particle size -100
105 g of mesh) was gradually fed and mixed while evaporating water for 1 hour.

Put this molten mixture into an aluminum container 12
It was left to cool and solidify for a while.

Table 1 shows the measurement results of the physical properties of the solidified material. Compared to the solidified material obtained by the conventional method of asphalt and radioactive waste treated under similar conditions, it has a higher specific gravity, less changes in weight when immersed in ion-exchanged water, and is softer. The point increases, indicating that the solidified material has stable properties and can be disposed of in the ocean.

Example 2 675 g of pelleted polyethylene (specific gravity 1.03),
Reactor cooling water filtration aid (specific gravity 1.00, specific radioactivity 6.
O uCi/TLl) 2 2 5 g and slag discharged from the zinc volatilization furnace during the dry zinc smelting process (specific gravity 3.
3, Fe203 38%, Sin232%, AI203
12, Ca0 1 1%, viscosity -20 mesh)
398 g were simultaneously charged into an extruder (extruder) from the hopper and melted and mixed while maintaining the temperature at 190°C.Then, the molten mixture was taken out into a cylindrical iron container and allowed to stand for 12 hours at room temperature. After cooling, remove the solidified material. Physical properties were measured.

As shown in Table 2, the results are as follows: Compared to the solidified material of polyethylene with a furnace auxiliary agent produced by the conventional method produced under similar conditions, the specific gravity increased, and both the weight and volume changed less when immersed in ion-exchanged water. Compressive strength, which is a mechanical property, improves,
This shows that ocean disposal is possible.

Example 3 Pellet polyethylene 560g (specific gravity 1.03
), powdered ion exchange resin used for radioactive waste liquid treatment,
A mixture of furnace auxiliary agent and granular ion exchange resin (specific gravity 1.02
) 240g (specific radioactivity 5.5 uCi/ml) and smelting slag (specific gravity 3.5,
Fe2034 5%, Si0238%, AI 2035
%, Ca08%, particle size -35 mesh. ．． :L) 370g
Mixed for 30 minutes using a commercially available mixer, then placed in an electric heating melting furnace and stirred at 180°C to melt for 30 minutes.
After 1.5 hours of mixing and melting with stirring using an impeller,
The material was collected from the furnace in the same manner as in Example 2, and after 10 hours, the solidified material was taken out and its physical properties were measured.

Table 3 shows the results.Compared to the conventional solidified material of polyethylene and radioactive waste tested under similar conditions, the specific gravity is lower, and the volumetric weight change due to immersion in ion-exchanged water is smaller, and the compressive strength is lower. In addition, the surface dose rate of the assimilated material was reduced, and it showed excellent performance as a solidified material for marine waste disposal.

Claims (1)

[Claims] 1. A method for treating solid radioactive waste, which comprises melting and mixing three types of materials: solid radioactive waste, asphalt or thermoplastic synthetic resin, and dry nonferrous metal brick slag, and cooling and solidifying the mixture.